What is osteonecrosis?

➢ Refers to infarction (ischemic necrosis) of bone and marrow cells. ➢ Diverse set of conditions predisposes to bone ischemia : vascular injury (trauma, vasculitis), drugs (corticosteroids), systemic disease (sickle cell crisis), and radiation. ➢ In about 25% of cases, the cause is unknown ➢ Microscopically, dead bone is recognized by empty lacunae surrounded by necrotic adipocytes that frequently rupture. ➢ In the healing response, osteoclasts resorb the necrotic trabeculae. ➢ Trabeculae that remain act as scaffolding for the deposition of new bone in a process known as creeping substitution ➢ ostéocytes nuclei are absent ➢ Bone trabeculae irregular ➢ fibrous tissue with nuclear debris in the medullary spaces